Lubricating Grease Composition

ABSTRACT

A lubricating grease composition for a polyamide resin member is used to be supplied as a lubricant on a surface of at least a sliding portion of the polyamide resin member including the sliding portion with an other member. The lubricating grease composition for a polyamide resin member contains a base oil which is a synthetic hydrocarbon oil, and a thickener which is at least one metal complex soap of a barium complex soap and a lithium complex soap, wherein a kinetic viscosity at 40° C. of the base oil ranges from 30 to 200 mm 2 /s and a drop point of the thickener is 270° C. or more.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of International Patent Application No. PCT/JP2016/054892 filed on Feb. 19, 2016, which claims priority to Japanese Patent Application No. 2015-066850, filed on Mar. 27, 2015. The contents of these applications are incorporated herein by reference in their entirety.

BACKGROUND Technical Field

The present disclosure relates to a lubricating grease composition for a polyamide resin member used to be supplied as a lubricant on the surface of at least a sliding portion of a polyamide resin member including the sliding portion where, for example, the other member comprising a resin member or a metal material slides or which slides on the other member.

Background Art

Heretofore, greases have been used as lubricant compositions in various industrial fields such as steels, automobiles, general machineries, and precision instruments. In recent years, polyamide resins have been commonly used as the member for sliding portions, and the like, of automobile parts, and the like, for the purpose of improving heat resistance in light of being used under a high-temperature environment in addition to weight saving and cost saving.

The lubricating grease used at the sliding portion of the polyamide resin member is needed to have a property which does not cause the deterioration (embrittlement) of the polyamide resin member in addition to lubricity, low-temperature performance and heat resistance. However, when a lithium soap grease or a urea grease commonly used is used as the lubricating grease for a polyamide resin member, attacking properties against the polyamide resin member used under a high-temperature (e.g., 150° C.) environment are expressed and deteriorate the polyamide resin member, resulting in tending to cause a problem of ruining the performance of machine parts made of the polyamide resin. Specifically, the lithium soap grease tends to be oxidized and deteriorate the polyamide resin member, and the urea grease itself has high heat resistance but when the resin is immersed under high-temperature environment as described above, a part of the amine in urea is eliminated and the eliminated amine expresses attacking properties against the polyamide resin member, resulting in tending to deteriorate the polyamide resin.

For example, Japanese Patent Application Publication No. 2012-102191 describes a lubricant composition, for the purpose of inhibiting the deterioration of the polyamide resin member under a high-temperature (140° C. in Examples) environment, containing a synthetic hydrocarbon oil, a urea-based thickener and zinc stearate and further at least one compound selected from the group consisting of trimellitic acid esters, aromatic sulfonamides, phthalic acid esters and hindered phenols.

However, as described above, the lubricant composition containing the urea-based thickener described in Japanese Patent Application Publication No. 2012-102191 expresses attacking properties against the polyamide resin member under a high-temperature environment and deteriorates the polyamide resin member, resulting in pose of a problem of decreasing the performance of machine parts made of the polyamide resin, particularly a breaking elongation.

Thus, This present disclosure is related to providing a lubricating grease composition for a polyamide resin member capable of inhibiting the deterioration of the polyamide resin member particularly under a high-temperature use environment while having good low-temperature properties by suitably adjusting a base oil and a thickener, thereby maintaining a breaking elongation at a high level without substantially decreasing it.

SUMMARY

Aspects of the present disclosure are as follows.

(1) A lubricating grease composition for a polyamide resin member used to be supplied as a lubricant on a surface of at least a sliding portion of the polyamide resin member including the sliding portion with an other member, wherein the lubricating grease composition for a polyamide resin member comprises a base oil which is a synthetic hydrocarbon oil, and a thickener which is at least one metal complex soap of a barium complex soap and a lithium complex soap, wherein a kinetic viscosity at 40° C. of the base oil ranges from 30 to 200 mm²/s, and a drop point of the thickener is 270° C. or more.

(2) The lubricating grease composition for a polyamide resin member according to the above (1), wherein the base oil is a single oil of a poly-α-olefin or a mixed oil of the poly-a-olefin and an ethylene-α-olefin copolymer.

(3) The lubricating grease composition for a polyamide resin member according to the above (1) or (2), wherein the other member is a metal member.

The present disclosure thus enables the provision of the lubricating grease composition for a polyamide resin member capable of inhibiting the deterioration of the polyamide resin member particularly under a high-temperature use environment while having good low-temperature properties, thereby maintaining a breaking elongation at a high level without substantially decreasing it by containing a base oil which is a synthetic hydrocarbon oil and a thickener which is at least one metal complex soap of a barium complex soap and a lithium complex soap, wherein a kinetic viscosity at 40° C. of the base oil ranges from 30 to 200 mm²/s and a drop point of the thickener is 270° C. or more.

DETAILED DESCRIPTION

Next, embodiments of the present disclosure are described below.

The lubricating grease composition for a polyamide resin member according to the present disclosure is used to be supplied as a lubricant on the surface of at least a sliding portion of the polyamide resin member including the sliding portion with other member and has both good low-temperature properties and outstanding mechanical properties (particularly a breaking elongation) particularly under a high-temperature use environment.

Examples of the other members include resin materials and metal materials. The resin material may be resin materials having an identical composition to or a different composition from the polyamide resin member. Note that the lubricating grease composition of the present disclosure, when the other member is metal members, is preferable in term of rendering particularly remarkable effects for the use as a lubricant on the surface of the polyamide resin member.

The “high-temperature (use) environment” herein refers to an environment wherein an ambient temperature ranges from 130 to 150° C.

The lubricating grease composition of the present disclosure contains a base oil and a thickener.

(Base Oil)

In the present disclosure, the base oil is a synthetic hydrocarbon oil, and the kinetic viscosity at 40° C. of the base oil ranges from 30 to 200 mm²/s. This is because when a kinetic viscosity at 40° C. of the synthetic hydrocarbon oil is lower than 30 mm²/s, the deterioration of the polyamide resin member facilitates, whereas when such a viscosity is higher than 200 mm²/s, a torque at a low temperature (low-temperature torque) increases. Note that the base oil, when, for example, an ester-based synthetic oil or an ether-based synthetic oil is used other than the synthetic hydrocarbon oil, may adversely affect the resin members, and it is thus preferable that the base oil be constituted only by the synthetic hydrocarbon oil. Examples of the synthetic hydrocarbon oil include poly-α-olefins, ethylene-α-olefin copolymers and polybutene. Specific examples of the particularly preferable base oil constituted by the synthetic hydrocarbon oil include when the base oil is a single oil of a poly-α-olefin or when the base oil is a mixed oil of a poly-α-olefin and an ethylene-α-olefin copolymer.

In the present disclosure, the poly-α-olefin refers to a polymer obtained by homopolymerizing or copolymerizing monomers comprising one or two or more of α-olefins having three or more carbon atoms.

The α-olefin herein is not particularly limited but examples thereof include linear terminal olefins having preferably 3 to 30 carbon atoms, more preferably 4 to 20 carbon atoms, further preferably 6 to 16 carbon atoms. More specifically, propylene, 1-butene, 1-pentene, 1-hexene, and the like, are included.

It is preferable that the poly-α-olefin have a mixing ratio ranging from 67 to 91 mass % to the entire lubricating grease composition. Additionally, when the synthetic hydrocarbon oil is the mixed oil of the poly-α-olefin and an ethylene-α-olefin copolymer, it is preferable that the poly-α-olefin have a mixing ratio ranging from 69 to 86 mass % to the entire lubricating grease composition.

Note that the degree of polymerization of poly-α-olefin is not particularly limited and includes those usually termed the oligomers. Additionally, one of the poly-α-olefins may be used singly or two or more thereof may be used in mixutre.

In the present disclosure, the ethylene-α-olefin copolymer refers to a copolymer comprising, as the constituent monomers, ethylene and one or two or more of α-olefins having three or more carbon atoms.

The α-olefin in the ethylene-α-olefin copolymer herein is not particularly limited but examples thereof include linear terminal olefins having preferably 3 to 30 carbon atoms, more preferably 4 to 20 carbon atoms, further preferably 6 to 16 carbon atoms. More specifically, propylene, 1-butene, 1-pentene, 1-hexene, and the like, are included. Note that one of the poly-α-olefins may be used singly or two or more thereof may be used. Note that the ethylene-α-olefin copolymer may have any of the structures of random copolymer, alternating copolymer, periodic copolymer or block copolymer.

The number average molecular weight of the ethylene-α-olefin copolymer ranges from 40,000 to 200,000, and the weight average molecular weight of the ethylene-α-olefin copolymer ranges from 40,000 to 200,000.

When the synthetic hydrocarbon oil is the mixed oil of the poly-α-olefin and the ethylene-a-olefin copolymer, it is preferable that the ethylene-α-olefin copolymer have a mixing ratio ranging from 1.5 to 3.5 mass % to the entire lubricating grease composition. When a mixing ratio of the ethylene-α-olefin copolymer is less than 1.5 mass %, the base oil viscosity may not be increased to a desirable numerical value within the suitable range, whereas such the viscosity is more than 3.5 mass %, the base oil viscosity may be much higher than the suitable range.

(Thickener)

In the lubricating grease composition of the present disclosure, the thickener is at least one metal complex soap of a lithium complex soap and a barium complex soap in light of being highly heat resistant and not deteriorating the polyamide resin. Further, the drop point of the thickener is 270° C. or more in light of inhibiting the deterioration of the polyamide resin member under a high-temperature environment (during high-temperature endurance) of the lubricating grease composition and maintaining a high breaking elongation to the polyamide resin member. When a drop point of the thickener is less than 270° C., the lubricating grease composition may attack and deteriorate the polyamide resin member during high-temperature endurance.

The lithium complex soap herein refers to a soap obtained by saponifying a plurality of carboxylic acids or esters with a lithium hydroxide. Additionally, the barium complex soap herein refers to a soap obtained by saponifying a plurality of carboxylic acids or esters with a barium hydroxide.

Specific examples of the lithium complex soap or the barium complex soap include those obtained by reacting fatty acids such as stearic acid, oleic acid, palmitic acid, and/or hydroxy fatty acids having 12 to 24 carbon atoms including one or more hydroxyl groups in a molecule and at least one selected from the group consisting of aromatic carboxylic acids, aliphatic dicarboxylic acids having 2 to 20 carbon atoms (more preferably 4 to 12 carbon atoms) and carboxylic acid monoamides with, for example, a lithium compound such as lithium hydroxide, or a barium compound such as barium hydroxide.

The above hydroxy fatty acid having 12 to 24 carbon atoms is not particularly limited and examples thereof include 12-hydroxystearic acid, 12-hydroxylauric acid, 16-hydroxypalmitic acid, with 12-hydroxystearic acid being particularly preferable among these.

Examples of the aromatic carboxylic acid include benzoic acids, phthalic acids, isophthalic acids, terephthalic acids, trimellitic acids, pyromellitic acids, salicylic acids, p-hydroxybenzoic acids, and the like.

Further, the above aliphatic dicarboxylic acid having 2 to 20 carbon atoms is not particularly limited and examples thereof include oxalic acids, malonic acids, succinic acids, methylsuccinic acids, glutaric acids, adipic acids, pimelic acids, suberic acids, azelaic acids, sebacic acids, nonamethylenedicarboxylic acids, decamethylenedicarboxylic acids, undecanedicarboxylic acids, dodecanedicarboxylic acids, tridecanedicarboxylic acids, tetradecanedicarboxylic acids, pentadecanedicarboxylic acids, hexadecanedicarboxylic acids, heptadecanedicarboxylic acids, octadecanedicarboxylic acids, and the like, with adipic acids, pimelic acids, suberic acids, azelaic acids, sebacic acids, nonamethylenedicarboxylic acids, decamethylenedicarboxylic acids, undecanedicarboxylic acids, dodecanedicarboxylic acids, tridecanedicarboxylic acids, tetradecanedicarboxylic acids, pentadecanedicarboxylic acids, hexadecanedicarboxylic acids, heptadecanedicarboxylic acids, octadecanedicarboxylic acids, and the like, being preferably used. Of these, azelaic acids and sebacic acids are preferable.

Further, examples of the carboxylic acid monoamide include those in which one of the carboxyl groups of the above dicarboxylic acid is amidated. Preferable examples include those in which one of the carboxyl groups of azelaic acid or sebacic acid is amidated.

Examples of the amine to be amidated include aliphatic primary amines such as butylamine, amylamine, hexylamine, heptylamine, octylamine, nonylamine, decylamine, laurylamine, myristyl amine, palmityl amine, stearyl amine, and behenyl amine, aliphatic secondary amines such as dipropylamine, diisopropylamine, dibutylamine, diamylamine, dilaurylamine, monomethyl laurylamine, distearylamine, monomethyl stearylamine, dimyristylamine, and dipalmitylamine, aliphatic unsaturated amines such as allylamine, diallylamine, oleylamine, and dioleylamine, alicyclic amines such as cyclopropylamine, cyclobutylamine, cyclopentylamine, and cyclohexylamine, aromatic amines such as aniline, methylaniline, ethylaniline, benzylamine, dibenzylamine, diphenylamine, and α-naphthylamine, with hexylamine, heptylamine, octylamine, nonylamine, decylamine, laurylamine, myristyl amine, palmityl amine, stearylamine, behenyl amine, dibutylamine, diamylamine, monomethyl laurylamine, monomethyl stearylamine, oleylamine, and the like, being preferably used.

When the lithium complex soap or the barium complex soap is mixed, carboxylic acids and/or esters thereof and the above metal hydroxide may be fed to the base oil and saponified in the base oil to be mixed.

When the lithium complex soap or the barium complex soap is prepared by carrying out the saponification reaction in the base oil, it is preferable to use the combination of stearic acid and/or 12-hydroxystearic acid as the carboxylic acid and azelaic acid or sebacic acid and the like.

Note that when the saponification reaction is carried out in the base oil, a plurality of carboxylic acids and/or esters thereof and acid amide may be saponified simultaneously or may be saponified sequentially.

When the thickener is the lithium complex soap, the mixing ratio to the entire lubricating grease composition is preferably 8 to 18 mass %. When a mixing amount is less than 8 mass %, the degree of oil separation may increase likely decreasing the storage stability of the lubricating grease composition, whereas when such an amount is higher than 18 mass %, the low-temperature torque at a low temperature may increase.

When the thickener is the barium complex soap, the mixing ratio to the entire lubricating grease composition is preferably 27 to 33 mass %. When a mixing amount is less than 27 mass %, the degree of oil separation may increase likely decreasing the storage stability of the lubricating grease composition, whereas when such an amount is higher than 33 mass %, the low-temperature torque at a low temperature may decrease.

(Others)

To the grease composition, other additives such as an antioxidant, a rust preventive, an extreme pressure agent, an oily agent, and a viscosity index improver, which have been added to the greases can be added as necessary in a range within which the effects of the present disclosure are not affected.

Examples of the antioxidant include phenol-based antioxidants such as 2,6-ditertiary butyl-4-methylphenol and 4,4′-methylenebis(2,6-ditertiary butylphenol), amine-based antioxidants such as alkyl diphenylamine, triphenylamine, phenyl-α-naphthylamine, phenothiazine, alkylated phenyl-α-naphthylamine, and alkylated phenythiazine. Additionally, phosphorus-based antioxidants and sulfur-based antioxidants are also used.

Examples of the rust preventive include Ca salts or Na salts of aromatic sulfonic acids or saturated aliphatic dicarboxylic acids, fatty acids, fatty acid amines, alkylsulfonic acid metal salts, alkylsulfonic acid amine salts, oxidized paraffins, polyoxyalkyl ethers, and the like.

Examples of the extreme pressure agent include phosphorus-based compounds such as phosphate esters, phosphite esters, and phosphate ester amines, sulfur-based compounds such as sulfides, and disulfides, sulfur-based compound metal salts such as dialkyldithiophosphoric acid metal salts (excluding zinc salts) and dialkyldithiocarbamic acid metal salts, chlorine-based compounds such as chlorinated paraffins and chlorinated diphenyls, and organometallic compounds such as molybdenum dialkyldithiocarbamates (MoDTP), and the like.

Examples of the oily agent include fatty acids or esters thereof, higher alcohols, polyhydric alcohols or esters thereof, aliphatic esters, aliphatic amines, aliphatic monoglycerides, montan waxes, amide-based waxes, and the like.

Examples of the viscosity index improver include polymethacrylates, ethylene-propylene copolymers, polyisobutylenes, polyalkylstyrenes, styrene-isoprene hydrogenated copolymers, and the like.

The composition is prepared by a method wherein each of the above components are added in a predetermined amount and thoroughly kneaded using a triple roll or a high-pressure homogenizer.

EXAMPLES

Hereinafter, the present disclosure is described in further detail in reference with Examples but not limited to these Examples.

(Examples 1 to 7 and Comparative Examples 1 to 6)

(1) Preparation Method of Lubricating Grease Compositions

The preparation method of lubricating grease compositions was carried out by the following method.

(1-1) Case in which the lithium complex soap (Li-Comp) was used as the thickener

First, the base oil and 12-hydroxystearic acid (thickener component) and lithium hydroxide (thickener component) were mixed in predetermined amounts in a mixing and stirring tank and stirred with heating at about 80 to 130° C. to carry out the saponification reaction. Further, azelaic acid (thickener component) was mixed in a predetermined amount and stirred with heating at about 80 to 200° C., to which lithium hydroxide (thickener component) was further added to carry out the saponification reaction, followed by cooling to produce a gelatinous substance. Each of the additives was added to the produced gelatinous substance, stirred and subsequently passed through a roll mill or a high-pressure homogenizer to prepare lubricating grease compositions containing each of the components shown below in the mixing amounts (mass %) shown in Table 1 and Table 2. The saponification reaction was carried out for 1 hour or more for the lubricating grease composition with which thickener A was mixed and less than 30 minutes for the lubricating grease composition with which thickener E was mixed. Note that the amount of each component constituting the thickeners A, E mixed was, in both thickeners, 63.5 mass % of 12-hydroxystearic acid, 19 mass % of azelaic acid and 17.5 mass % of lithium hydroxide, to the total amount of the thickener.

(1-2) Case in which the barium complex soap (Ba-Comp) was used as the thickener

First, the base oil and sebacic acid (thickener component) and carboxylic acid monostearyl amide (thickener component) were mixed in predetermined amounts in a mixing and stirring tank and stirred with heating at about 80 to 200° C., to which barium hydroxide (thickener component) was added to carry out the saponification reaction, followed by cooling to produce a gelatinous substance. Each of the additives was added to the produced gelatinous substance, stirred and subsequently passed through a roll mill or a high-pressure homogenizer to prepare lubricating grease compositions containing each of the components shown below in the mixing amounts (mass %) shown in Table 1 and Table 2. The saponification reaction was carried out for 30 minutes or more for the lubricating grease composition with which thickener B was mixed and less than 15 minutes for the lubricating grease composition with which thickener F was mixed. Note that the amount of each component constituting the thickeners B, F mixed was, in both thickeners, 27.5 mass % of sebacic acid, 41.5 mass % of carboxylic acid monostearyl amide and 31 mass % of barium hydroxide, to the total amount of the thickener.

(1-3) Case in which the lithium soap (Li-OHST) was used as the thickener

First, the base oil and 12-hydroxystearic acid (thickener component) and lithium hydroxide (thickener component) were mixed in predetermined amounts in a mixing and stirring tank and stirred with heating at about 80 to 130° C. to carry out the saponification reaction. The mixture was further stirred with heating to a melting temperature and subsequently cooled to produce a gelatinous substance. Each of the additives was added to the produced gelatinous substance, stirred and subsequently passed through a roll mill or a high-pressure homogenizer to prepare lubricating grease compositions containing each of the components shown below in the mixing amounts (mass %) shown in Table 2. Note that the amount of each component constituting the thickener C mixed was 88 mass % of 12-hydroxystearic acid and 12 mass % of lithium hydroxide, to the total amount of the thickener.

(1-4) Case in which Urea was used as the thickener

First, the base oil and diphenylmethane diisocyanate (thickener component) and octylamine (thickener component) were stirred with heating at 70 to 180° C. to carry out the reaction, and the temperature was elevated and cooled to produce a gelatinous substance. Each of the additives was added to the produced gelatinous substance, stirred and subsequently passed through a roll mill or a high-pressure homogenizer to prepare lubricating grease compositions containing each of the components shown below in the mixing amounts (mass %) shown in Table 2. Note that the amount of each component constituting the thickeners D mixed was 50 mass % of diphenylmethane diisocyanate and 50 mass % of octylamine, to the total amount of the thickener.

Poly-α-olefin A: 40° C. kinetic viscosity 30 mm²/s (a product of INEOS Oligomers Japan DURASYN 166)

Poly-α-olefin B: 40° C. kinetic viscosity 46 mm²/s (a product of INEOS Oligomers Japan DURASYN 168)

Poly-α-olefin C: 40° C. kinetic viscosity 5 mm²/s (a product of INEOS Oligomers Japan DURASYN 162)

Poly-α-olefin D: 40° C. kinetic viscosity 400 mm²/s (a product of INEOS Oligomers Japan DURASYN 174)

Ethylene-α-olefin copolymer: number average molecular weight 68000, weight average molecular weight 147000 (a product of SHOWA VARNISH CO., LTD. L6Z-25)

Thickener A: Li-Comp having a drop point at 280° C. (lithium complex soap)

Thickener B: Ba-Comp having a drop point at 270° C. (barium complex soap)

Thickener C: Li-OHST having a drop point at 200° C. (lithium soap)

Thickener D: Urea having a drop point at 270° C. (urea)

Thickener E: Li-Comp having a drop point at 255° C. (lithium complex soap)

Thickener F: Ba-Comp having a drop point at 230° C. (barium complex soap)

Antioxidant: Phenylnaphthylamine (a product of SANYO CHEMICAL INDUSTRIES, Ltd. VANLUBE 81)

Rust preventive: neutral calcium sulfonate (a product of KING Industries, Inc., NA SUL CA 1089)

(2) Evaluation Method

(2-1) Base oil viscosity

The base oil viscosity was measured in accordance with JIS K2283: 2000.

(2-2) Worked penetration

The worked penetration was measured in accordance with JIS K2220. 7: 2013.

(2-3) Drop point

The drop point was measured in accordance with JIS K2220. 8: 2013.

(2-4) Low-temperature property (low-temperature torque)

In accordance with JIS K2220. 18: 2013, the maximum torque (starting torque) at −40° C. obtained at the run-up time was measured. In the present disclosure, a numerical value (index) of the starting torque of 27 or less was defined as the passing level, whereas such a value of more than 27 was defined as failure.

(2-5) Compatibility of the resin with the grease composition under a high temperature use environment (breaking elongation)

The grease was applied in a thickness of about 1 mm to the surface of Nylon 66 (registered trademark) as a test specimen prescribed in JIS K7162: 1994, the test specimen was allowed to stand in a thermostat at 150° C. for 500 hours, subsequently the lubricant was wiped off, and the tensile test prescribed in JIS K7162 (Plastics—Determination of Tensile Properties—Part 1: General principles) was carried out to measure a breaking elongation. In the present disclosure, a breaking elongation of 30% or more was defined as the passing level, whereas such an elongation of less than 30% was defined as failure.

(3) Evaluation Results

The evaluation results on the low-temperature properties (low-temperature torque) and the high-temperature properties (breaking elongation) when each of the lubricating grease compositions was applied to the polyamide resin member are shown in Table 1 and Table 2.

TABLE 1 Example No. 1 2 3 4 5 6 7 Base oil Poly-α-olefin A 84.4 — 84.9 — 67.4 69.4 90.4 Poly-α-olefin B — 82.4 — 85.6 — — — Ethylene-α-olefin copolymer — — 1.5 2.8 — 2 — Thickener Thickener A 15 17 13 11 — — 9 Thickener B — — — — 32 28 — Other Antioxidant 0.5 0.5 0.5 0.5 0.5 0.5 0.5 additives Rust preventive 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Total (mass %) 100 100 100 100 100 100 100 Base oil 40° C. kinetic viscosity (mm²/s) 30 46 100 200 30 46 30 Worked penetration of lubricating grease 265 255 275 290 275 295 310 Drop point of thickener (° C.) 280 280 275 280 270 270 280 Performance Low-temperature property: −40° C. 16 21 16 19 25 27 13 starting torque Resin compatibility: 32 30 33 32 40 43 31 breaking elongation (%)

TABLE 2 Comparative Example No. 1 2 3 4 5 6 Base oil Poly-α-olefin A  84.4  69.4  88.4  86.4 — — Poly-α-olefin C — — — —  84.4 — Poly-α-olefin D — — — — —  84.4 Thickener Thickener A — — — —  15  15 Thickener B — — — — — — Thickener C — —  11 — — — Thickener D — — —  13 — — Thickener E  15 — — — — — Thickener F —  30 — — — — Other Antioxidant  0.5  0.5  0.5  0.5  0.5  0.5 additives Rust preventive  0.1  0.1  0.1  0.1  0.1  0.1 Total (mass %) 100 100 100 100 100 100 Base oil 40° C. kinetic viscosity (mm²/s)  30  30  30  30  5 400 Worked penetration of lubricating grease 280 260 270 285 275 265 Drop point of thickener (° C.) 255 230 200 270 280 280 Performance Low-temperature property: −40° C.  15  24  14  16  12  45 starting torque Resin compatibility:  21  22  10  22  24  30 breaking elongation (%) (Note) The underlines at the numerical values in Table 2 indicate that the values are outside the suitable range of the present disclosure and the performance failed to achieve the passing level.

From the evaluation results shown in Table 1, all of Examples 1 to 7 maintained the starting torques at −40° C. as low as 13 to 27 and the breaking elongations as high as 30 to 43%, thereby revealing good compatibility of the polyamide resin member with the grease compositions.

In contrast, from the evaluation results shown in Table 2, all of Comparative Examples 1 to 6 failed to achieve the passing levels of numerical values in either of the starting torque at −40° C. or the breaking elongation.

The present disclosure thus enables the provision of the lubricating grease composition for a polyamide resin member capable of inhibiting the deterioration of the polyamide resin member particularly under a high-temperature use environment while having good low-temperature properties, thereby maintaining a breaking elongation at a high level without substantially decreasing it. The lubricating grease composition of the present disclosure is suitable to be used at a sliding portion of various machine parts constituting automobile, machine, electrical and electric equipment, and the like, that use resin materials such as polyamide resins. Specifically, in an automobile, examples include rolling bearings, sliding bearings and gear parts and cam parts of automobile accessories such as electric radiator fan motors, fan couplings, electronically controlled EGR, electronically controlled throttle valves, alternators, and electric power steerings, to which the lubricity is demanded. 

1. A lubricating grease composition for a polyamide resin member used to be supplied as a lubricant on a surface of at least a sliding portion of the polyamide resin member including the sliding portion with an other member, wherein the lubricating grease composition for a polyamide resin member comprises: a base oil which is a synthetic hydrocarbon oil; and a thickener which is at least one metal complex soap of a barium complex soap and a lithium complex soap, wherein a kinetic viscosity at 40° C. of the base oil ranges from 30 to 200 mm²/s, and a drop point of the thickener is 270° C. or more.
 2. The lubricating grease composition for a polyamide resin member according to claim 1, wherein the base oil is a single oil of a poly-α-olefin or a mixed oil of the poly-α-olefin and an ethylene-α-olefin copolymer.
 3. The lubricating grease composition for a polyamide resin member according to claim 1, wherein the other member is a metal member. 